Carbon-based materials on the earth are maintained at a constant amount and balanced while forming carbon cycles in various forms. However, due to the increase in atmospheric carbon dioxide (CO2) which is one of the materials forming carbon cycles, such a balance is being broken. According to the National Oceanic and Atmospheric Administration (NOAA)'s report of trend in atmospheric CO2, the concentration of atmospheric CO2 before industrialization remained at about 280 ppm (parts per million), but has geometrically increased after industrialization and exceeded about 350 ppm in 1989 and then has steadily increased and exceeded the maximum limit, i.e., about 400 ppm, in May 2012 and remained at a monthly average of about 400 ppm as of April 2014.
The increase in concentration of atmospheric CO2 has been caused by the increase in CO2 emissions after industrialization, and the CO2 emissions have continuously increased since the first measurement in 1965 (about 12 billion tons), and as of 2012, more than about 34 billion tons of CO2 has been emitted a year. In the current system largely depending on fossil fuels as energy, the increase in CO2 emissions is expected to continue.
The CO2 emissions are problems not only for other countries. Korea has also much contributed to CO2 emissions, and according to the result of analyzing the report [LONG-TERM TREND IN GLOBAL CO2 EMISSIONS] prepared by the Joint Research Centre (JRC) and the Netherlands Environment Assessment Agency (PBL), the CO2 emissions in Korea have also increased by about 136% in the last 20 years and the rate of increase is the third highest in the world, following China (about 256%) and India (about 179%), Further, the CO2 emissions in Korea was ranked ninth in the world in 2008 and rose to eighth place in 2009 and also rose to seventh place in the world in 2010 and have remained in that place ever since.
The biggest problem caused by the increase in atmospheric CO2 is global warming. The Intergovernmental Panel on Climate Change (IPCC) diagnosed that all the countries of the world have been unwilling to deal with climate change and if CO2 emissions cannot be suppressed in the next 15 years, the climate change problem would be worsened to a level which cannot be actually solved by current technology. As such, with awareness of the danger of the rapid increase in atmospheric CO2, studies for removing atmospheric CO2 are being actively conducted around the world.
As a technology for removing atmospheric CO2, Carbon Capture and Storage (CCS) has been actively studied till recently. However, CCS needs a wide space to store captured CO2 and also has a risk caused by the storage of a large amount of CO2 in one place. Due to this problem, Carbon Capture and Utilization (CCU) technology capable of directly converting captured CO2 into useful materials without storage has received a lot of attention in recent years. The CCS is a technology of burying and discarding the captured CO2 as waste resource, whereas the CCU is a technology of recycling the captured CO2 into a high-value product. Since CO2 is the most abundant carbon source on the earth, various technologies for converting CO2 into useful materials are being studied.
Currently, recycling of CO2 is being studied mainly in the fields of converting CO2 into useful chemicals such as acetate, polycarbonate, and the like through a catalytic method [Korean Patent Laid-open Publication No. 10-2008-0016198], producing bio fuels using living organisms such as microalgae, producing renewable fuels such as methanol using water and CO2 through artificial photosynthesis, and producing construction materials such as cement by reacting CO2 with calcium salt or magnesium salt to be converted into minerals according to a natural rock formation process occurring in clams or oysters. As such, recycling of CO2 is being studied in various fields.
As a technology for converting CO2 into useful materials, an electrochemical conversion method is also being studied. The electrochemical conversion of CO2 is a kind of catalytic method and uses electric energy to convert CO2 through an electrode reaction, and can convert CO2 at relatively room temperature and atmospheric pressure, uses a simple device, and can also selectively produce a product depending on the kind of a working electrode used in the system, and, thus, it is an effective method of converting CO2.